Trait‐mediated effects driven by an invasive herbivore alter functionally diverse plant–frugivore interactions

Abstract Fruit traits play a fundamental role in mediating plant‐frugivore interactions, shaping seed dispersal dynamics. Given the complexity of multi‐species interactions, these traits and, consequently, plant‐frugivore interactions can be indirectly influenced by third‐party species, leading to trait‐mediated effects. While herbivory is demonstrated to alter some fruit traits through resource allocation shifts or compensatory responses, its impact on plant‐frugivore interactions remains largely unexplored. We examined whether herbivory by the invasive palm borer Paysandisia archon (Lepidoptera, Castniidae) influences fruit attractiveness and alters plant‐frugivore interactions in the Mediterranean dwarf palm Chamaerops humilis (Arecaceae). Across four sites in Mallorca (Balearic Islands, W. Mediterranean Sea), we characterized fruit and seed traits and monitored visitation and fruit removal rates by functionally diverse frugivores on intact and infested female palms over two consecutive seasons. Intensely moth‐infested palms (i.e. those with 60% of the stems infested) produced 1.7‐fold rounder fruits with 1.3‐fold lower pulp content than those of intact palms. Surprisingly, the frequency of fruit removal by legitimate seed dispersers was six times higher and overall fruit removal occurred 10 times faster in infested palms compared to intact ones. However, infested palms also experienced a 2.4 and 3‐fold increases in pulp removal by invertebrates and seed predation by scolytine beetles, respectively. Our findings reveal a trade‐off whereby herbivory‐driven changes in fruit traits (i.e. rounder fruits with lower pulp content) enhance the attraction of both mutualistic (seed dispersers) and antagonistic (pulp feeders and seed predators) frugivores, but with markedly different strength. These contrasting yet asymmetrical responses emphasize the importance of accounting for frugivore functional diversity, as plant fitness ultimately depends on the balance between mutualistic and antagonistic interactions. Herbivory thus has the potential to reshape plant‐frugivore interactions and influence the long‐term eco‐evolutionary dynamics of plant populations. Read the free Plain Language Summary for this article on the Journal blog.